标题： 观察者在圆周运动中的命运 显示英文标题

标题： The fate of observers in circular motion

摘要： 在牛顿物理学或广义相对论中，能量耗散导致沿圆轨道运动的观察者缓慢地螺旋向引力场的源头靠拢。我们展示，在任何尊重弱等效原理的引力理论中，能量的损失具有相同的效果，通过揭示一个关于大质量检验粒子的能量与其轨道稳定性之间密切的关系。最终，大质量粒子要么坠落，要么被驱使向广义牛顿势的极小值靠拢，在那里它们变得静止。此外，我们构建了一个玩具度规，该度规展示了一个无界的最内层稳定圆轨道，允许到达这一轨道的粒子被排斥开来。 显示英文摘要

摘要： In Newtonian physics or in general relativity, energy dissipation causes observers moving along circular orbits to slowly spiral towards the source of the gravitational field. We show that the loss of energy has the same effect in any theory of gravity respecting the weak equivalence principle, by exhibiting an intimate relation between the energy of a massive test particle and the stability of its orbit. Ultimately, massive particles either plunge, or are driven towards minima of the generalized Newtonian potential, where they become static. In addition, we construct a toy metric which displays an unbound innermost stable circular orbit, allowing particles that reach this orbit to be expelled away.